I. Field of the Invention
This invention relates generally to the field of physical exercise performed in accordance with a prescribed training program, and more particularly, to a method for effectively utilizing the measured aerobic capacity of a subject to develop, monitor progress using, and accordingly modify an exercise training program, using an ergometer to optimally achieve an increase in the size of the physical training effect to more effectively motivate the subject to complete the exercise training program, and to reduce the cost of providing exercise training programs.
II. Discussion of the Prior Art
It is well-recognized that physical exercise can be used to increase the physical well being of individuals whose health ranges from that of being simply "out of shape" to that of having some form of hemodynamic or respiratory dysfunction. However, it is also known that whereas over-exertion can be dangerous and even life-threatening, exercise below a certain intensity may prove to be ineffective in improving exercise tolerance.
Various forms of exercise machines are known in the art. Devices of the class commonly referred to as ergometers are adapted to allow a user to work against a force and to displace that force through a distance, i.e., perform work. Devices of the class include stair-climbing machines, treadmills, and the like. Typical of such devices is the so-called bicycle ergometer in which the user pedals a stationary device so as to drive a flywheel. The amount of effort expended is determined by the mass of the flywheel as well as the setting of friction pad brakes normally coacting with the flywheel.
Ergometers which use an electrically controllable element to directly assist or resist the force applied by the user and to dissipate the energy applied by the user are known. These include computer-controlled, motor-assisted cycle ergometers which can provide a dynamic range of power dissipation. One such device that controls the armature field current to determine power dissipation over a range between 0 and 350 watts at a constant 60 rpm pedaling speed is described by Sherrill et al, IEEE Trans on Bio-Med Engineering, Volume BME 28, No. 10 (1987). That system is calibrated at a certain speed or speeds and is not accurate at speeds other than those for which it is calibrated so that it does not allow the operator to independently select the most comfortable pedaling rate. A torque/speed related feedback control system is described in Gause et al (U.S. Pat. No. 3,744,480). That system has a manual set-point in the direct work measuring mode.
Further, U.S. Pat. Nos. 4,261,562; 4,082,267; 3,848,467; 4,822,036; and 4,750,738 all disclose the use of a dynamoelectric machine such as an electric motor or generator for controlling the speed of the apparatus and dissipating the energy input by the user. U.S. Pat. No. 4,842,274 to Oosthuizen et al discloses a variant of this approach in which an hydraulic clutch is interposed between the dynamoelectric machine and the movable element of the apparatus. It is further known to control the operation of a motor-assisted cycle ergometer device based on work as related to a target or programmed heart rate in relation to the observed real time heart rate of the operator. Such a programmable control system is also disclosed by Gause et al in the above-cited U.S. Pat. No. 3,744,480. Nakao et al (U.S. Pat. No. 4,790,528) describe a rehabilitation training device in the form of a motor-assisted cycle ergometer which is controlled in a manner such that the pedaling resistance load is varied based on the actual monitored heart rate of the operator in relation to a target value.
An ideal example of an ergometer usable with the present invention has been described by Boyd in copending patent application Ser. No. 07/801,252. In that device, the actual energy imparted by the user into the system is measured and compared to a setpoint. The resistance can then be varied so that the actual energy input of the exerciser matches that specified by the setpoint, independent of the speed of pedaling by the exerciser.
All of these prior devices are designed to monitor or control one aspect of an exercise training program. Ergometers of all varieties simply vary the resistance to the exerciser in some fashion so that energy can be expended by the exerciser according to an establish setpoint and absorbed by the ergometer.
Cardiopulmonary exercise stress tests have long been used to measure aerobic capacity. A cardiopulmonary exercise stress testing system, of course, simply measures oxygen consumption (VO.sub.2), carbon dioxide production (VCO.sub.2), ventilation (VE), heart rate (HR) and blood pressure (BP); and from those measurements, one can derive maximum aerobic capacity (VO.sub.2 max) and an exhaustion index (anaerobic threshold) of a subject.
A further multi-function cardiopulmonary exercise system is shown in Anderson et al (U.S. Pat. No. 4,463,754). That system includes a microprocessor-based waveform analyzer for performing a real time breath-by-breath analysis of cardiopulmonary activity to measure a plurality of parameters including stress testing for diagnosing and to ascertain physical fitness. While this device is an excellent source of evaluation data, it clearly does not function as a training or rehabilitation system.
Presently, these are used independently and there is no link between the physiologic measurements of aerobic fitness--VO.sub.2 max and anaerobic threshold--and the tools of physical training-- ergometers. The importance of such a linkage has received increasing attention in the medical literature. It is known that exercise training stimulates changes in the exercising muscles, which increase capillary density, the number of mitochondria, and the concentration of aerobic enzymes. These changes act to increase the capacity for aerobic work and forestall the onset of lactic acidosis. Casaburi et al have reported that an exercise program in which subjects are exercised at workrate intensities at or above the workrate intensity at which the anaerobic threshold occurs can achieve a marked improvement in aerobic capacity. "Reductions in Exercise Lactic Acidosis and Ventilation as a Result of Exercise Training in Patients with Obstructive Lung Disease", (Am Rev Respir Dis, 1991; 143:9-18). In another study by Coplan et al, "Using Exercise Respiratory Measurements to Compare Methods of Exercise Prescription" (Am J Cardiol, 1986; 58:832-836), it was stated that exercise prescriptions based upon anaerobic threshold are preferable to exercise prescriptions based upon predicted maximal heart rate. It is well established that sustained exercise at intensities approaching the work rate intensity at VO.sub.2 max is impossible, and possibly dangerous.
From the above, it will readily be observed, then, that workrate, in fact, is the independent variable of both a cardiopulmonary stress test and of an exercise training program, and that the dependent physiological variables including workrate, oxygen uptake or consumption (VO.sub.2), carbon dioxide production (VCO.sub.2), ventilation (VE), heart rate (HR) and blood pressure (BP), will remain unchanged unless exercise training is used to effect change. Moreover, it becomes apparent that using HR, for example, as a physiologic setpoint to control the workrate, or exercise intensity, of an ergometer clearly does not logically follow. In other words, the scientific method does not teach the use of a dependent variable (HR) to control the value of an independent variable (workrate). In accordance with the present invention, a more rational approach, and one that more closely adheres to the scientific method, is one that uses workrate as the independent variable of an exercise training program and the dependent physiologic variables as measurements of the efficacy of the exercise training program.
Moreover, to insure efficacy of an exercise training program, aspects other than purely physiologic factors need to be taken into account when designing a protocol for and measuring the achievements resulting from the exercise training program. It is important that the physician or medical professional be provided with sufficient data to fairly assess patient compliance with the program and the psychological acceptability of the exercise protocol. The many factors involved in properly gauging the success of the exercise training program, heretofore, has required that the exercise program be carried out in a health provider's office or clinic where the intensity of exercise could be adjusted while the physiologic, psychologic, and compliance factors could be directly observed. This, of course, greatly increases the cost of implementing the exercise training program.
While both the techniques and tools exist for implementing an exercise training program which can be both productive and safely tolerated by the exercising subject, no satisfactory method, or tools to implement the method, has been available for (1) producing an exercise training protocol for an ergometer which can be faithfully reproduced by the subject, independent of his pedal speed, (2) providing an off-line monitoring capability for the prescribing physician or medical professional to determine exercise protocol compliance and to determine the physiologic and psychologic adaptation of the subject to the protocol, (3) providing relevant, easy to understand information to the exercising subject to visualize the achievements the subject is making during the training program so as to better motivate the subject to continue the exercise training program to completion, and (4) increasing, or decreasing, the duration and/or intensity of the exercise training protocol over time as a function of measured and monitored physiologic and psychologic variables.
As used herein, the term "protocol" refers to the programmed variation of a target workrate over a predetermined exercise time period used for repeated sessions in an exercise program which, in turn, consists of a predetermined number of such sessions over a program time period. The preferred protocol is in the form of a two-dimensional array of values where one dimension is workrate and the other dimension is time. A protocol can be displayed as either a table of numbers or as a graphical plot. The preferred method is by presenting the protocol as a graphical plot of workrate v. time. A display of this type is believed easier to interpret and understand.